[libvirt PATCH v3 06/18] qemu: implement persistent file cache for nbdkit caps

[Jonathon Jongsma]

Implement the loadFile and saveFile virFileCacheHandlers callbacks so
that nbdkit capabilities are cached perstistently across daemon
restarts. The format and implementation is modeled on the qemu
capabilities, but simplified slightly.

Signed-off-by: Jonathon Jongsma <jjongsma at redhat.com>
---
 src/qemu/qemu_nbdkit.c | 234 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 232 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_nbdkit.c b/src/qemu/qemu_nbdkit.c
index 9ab048e9e1..a47e169a0f 100644
--- a/src/qemu/qemu_nbdkit.c
+++ b/src/qemu/qemu_nbdkit.c
@@ -317,11 +317,241 @@ virNbdkitCapsNewData(const char *binary,
 }
 
 
+static int
+qemuNbdkitCapsValidateBinary(qemuNbdkitCaps *nbdkitCaps,
+                             xmlXPathContextPtr ctxt)
+{
+    g_autofree char *str = NULL;
+
+    if (!(str = virXPathString("string(./path)", ctxt))) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("missing path in nbdkit capabilities cache"));
+        return -1;
+    }
+
+    if (STRNEQ(str, nbdkitCaps->path)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("Expected caps for '%s' but saw '%s'"),
+                       nbdkitCaps->path, str);
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static int
+qemuNbdkitCapsParseFlags(qemuNbdkitCaps *nbdkitCaps,
+                         xmlXPathContextPtr ctxt)
+{
+    g_autofree xmlNodePtr *nodes = NULL;
+    size_t i;
+    int n;
+
+    if ((n = virXPathNodeSet("./flag", ctxt, &nodes)) < 0) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("failed to parse qemu capabilities flags"));
+        return -1;
+    }
+
+    VIR_DEBUG("Got flags %d", n);
+    for (i = 0; i < n; i++) {
+        unsigned int flag;
+
+        if (virXMLPropEnum(nodes[i], "name", qemuNbdkitCapsTypeFromString,
+                           VIR_XML_PROP_REQUIRED, &flag) < 0)
+            return -1;
+
+        qemuNbdkitCapsSet(nbdkitCaps, flag);
+    }
+
+    return 0;
+}
+
+
+/*
+ * Parsing a doc that looks like
+ *
+ * <nbdkitCaps>
+ *   <path>/some/path</path>
+ *   <nbdkitctime>234235253</nbdkitctime>
+ *   <plugindirmtime>234235253</plugindirmtime>
+ *   <filterdirmtime>234235253</filterdirmtime>
+ *   <selfctime>234235253</selfctime>
+ *   <selfvers>1002016</selfvers>
+ *   <flag name='foo'/>
+ *   <flag name='bar'/>
+ *   ...
+ * </nbdkitCaps>
+ *
+ * Returns 0 on success, 1 if outdated, -1 on error
+ */
+static int
+qemuNbdkitCapsLoadCache(qemuNbdkitCaps *nbdkitCaps,
+                        const char *filename)
+{
+    g_autoptr(xmlDoc) doc = NULL;
+    g_autoptr(xmlXPathContext) ctxt = NULL;
+    long long int l;
+    unsigned long lu;
+
+    if (!(doc = virXMLParse(filename, NULL, NULL, "nbdkitCaps", &ctxt, NULL, false)))
+        return -1;
+
+    if (virXPathLongLong("string(./selfctime)", ctxt, &l) < 0) {
+        virReportError(VIR_ERR_XML_ERROR, "%s",
+                       _("missing selfctime in nbdkit capabilities XML"));
+        return -1;
+    }
+    nbdkitCaps->libvirtCtime = (time_t)l;
+
+    nbdkitCaps->libvirtVersion = 0;
+    if (virXPathULong("string(./selfvers)", ctxt, &lu) == 0)
+        nbdkitCaps->libvirtVersion = lu;
+
+    if (nbdkitCaps->libvirtCtime != virGetSelfLastChanged() ||
+        nbdkitCaps->libvirtVersion != LIBVIR_VERSION_NUMBER) {
+        VIR_DEBUG("Outdated capabilities in %s: libvirt changed "
+                  "(%lld vs %lld, %lu vs %lu), stopping load",
+                  nbdkitCaps->path,
+                  (long long)nbdkitCaps->libvirtCtime,
+                  (long long)virGetSelfLastChanged(),
+                  (unsigned long)nbdkitCaps->libvirtVersion,
+                  (unsigned long)LIBVIR_VERSION_NUMBER);
+        return 1;
+    }
+
+    if (qemuNbdkitCapsValidateBinary(nbdkitCaps, ctxt) < 0)
+        return -1;
+
+    if (virXPathLongLong("string(./nbdkitctime)", ctxt, &l) < 0) {
+        virReportError(VIR_ERR_XML_ERROR, "%s",
+                       _("missing nbdkitctime in nbdkit capabilities XML"));
+        return -1;
+    }
+    nbdkitCaps->ctime = (time_t)l;
+
+    if (virXPathLongLong("string(./plugindirmtime)", ctxt, &l) < 0) {
+        virReportError(VIR_ERR_XML_ERROR, "%s",
+                       _("missing plugindirmtime in nbdkit capabilities XML"));
+        return -1;
+    }
+    nbdkitCaps->pluginDirMtime = (time_t)l;
+
+    if (virXPathLongLong("string(./filterdirmtime)", ctxt, &l) < 0) {
+        virReportError(VIR_ERR_XML_ERROR, "%s",
+                       _("missing filterdirmtime in nbdkit capabilities XML"));
+        return -1;
+    }
+    nbdkitCaps->filterDirMtime = (time_t)l;
+
+    if (qemuNbdkitCapsParseFlags(nbdkitCaps, ctxt) < 0)
+        return -1;
+
+    if ((nbdkitCaps->version = virXPathString("string(./version)", ctxt)) == NULL) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("missing version in nbdkit capabilities cache"));
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static void*
+virNbdkitCapsLoadFile(const char *filename,
+                      const char *binary,
+                      void *privData G_GNUC_UNUSED,
+                      bool *outdated)
+{
+    g_autoptr(qemuNbdkitCaps) nbdkitCaps = qemuNbdkitCapsNew(binary);
+    int ret;
+
+    if (!nbdkitCaps)
+        return NULL;
+
+    ret = qemuNbdkitCapsLoadCache(nbdkitCaps, filename);
+    if (ret < 0)
+        return NULL;
+    if (ret == 1) {
+        *outdated = true;
+        return NULL;
+    }
+
+    return g_steal_pointer(&nbdkitCaps);
+}
+
+
+static char*
+qemuNbdkitCapsFormatCache(qemuNbdkitCaps *nbdkitCaps)
+{
+    g_auto(virBuffer) buf = VIR_BUFFER_INITIALIZER;
+    size_t i;
+
+    virBufferAddLit(&buf, "<nbdkitCaps>\n");
+    virBufferAdjustIndent(&buf, 2);
+
+    virBufferEscapeString(&buf, "<path>%s</path>\n",
+                          nbdkitCaps->path);
+    virBufferAsprintf(&buf, "<nbdkitctime>%lld</nbdkitctime>\n",
+                      (long long)nbdkitCaps->ctime);
+    virBufferAsprintf(&buf, "<plugindirmtime>%lld</plugindirmtime>\n",
+                      (long long)nbdkitCaps->pluginDirMtime);
+    virBufferAsprintf(&buf, "<filterdirmtime>%lld</filterdirmtime>\n",
+                      (long long)nbdkitCaps->filterDirMtime);
+    virBufferAsprintf(&buf, "<selfctime>%lld</selfctime>\n",
+                      (long long)nbdkitCaps->libvirtCtime);
+    virBufferAsprintf(&buf, "<selfvers>%lu</selfvers>\n",
+                      (unsigned long)nbdkitCaps->libvirtVersion);
+
+    for (i = 0; i < QEMU_NBDKIT_CAPS_LAST; i++) {
+        if (qemuNbdkitCapsGet(nbdkitCaps, i)) {
+            virBufferAsprintf(&buf, "<flag name='%s'/>\n",
+                              qemuNbdkitCapsTypeToString(i));
+        }
+    }
+
+    virBufferAsprintf(&buf, "<version>%s</version>\n",
+                      nbdkitCaps->version);
+
+    virBufferAdjustIndent(&buf, -2);
+    virBufferAddLit(&buf, "</nbdkitCaps>\n");
+
+    return virBufferContentAndReset(&buf);
+}
+
+
+static int
+virNbdkitCapsSaveFile(void *data,
+                      const char *filename,
+                      void *privData G_GNUC_UNUSED)
+{
+    qemuNbdkitCaps *nbdkitCaps = data;
+    g_autofree char *xml = NULL;
+
+    xml = qemuNbdkitCapsFormatCache(nbdkitCaps);
+
+    if (virFileWriteStr(filename, xml, 0600) < 0) {
+        virReportSystemError(errno,
+                             _("Failed to save '%s' for '%s'"),
+                             filename, nbdkitCaps->path);
+        return -1;
+    }
+
+    VIR_DEBUG("Saved caps '%s' for '%s' with (%lld, %lld)",
+              filename, nbdkitCaps->path,
+              (long long)nbdkitCaps->ctime,
+              (long long)nbdkitCaps->libvirtCtime);
+
+    return 0;
+}
+
+
 virFileCacheHandlers nbdkitCapsCacheHandlers = {
     .isValid = virNbdkitCapsIsValid,
     .newData = virNbdkitCapsNewData,
-    .loadFile = NULL,
-    .saveFile = NULL,
+    .loadFile = virNbdkitCapsLoadFile,
+    .saveFile = virNbdkitCapsSaveFile,
     .privFree = NULL,
 };
 
-- 
2.37.3